Important new feature is save-states. This gave me the means to finally finish the very first game I bought as a kid: Konami's Nemesis 2 for the MSX computer.
In these times games were usually hard. Nemesis 2 is even harder. The only way to play it without save-states is not dying all 15 levels. Given that Nemesis 2 is a shooter this is VERY hard :)
Each one of those red bullets and grey stones is fatal :)
But save-states wasn't enough. I also enabled "old-people" mode, meaning running the emulator at 75% speed of the original MSX computer.
After more then an hour of hard labour playing using alot of save-states I finally managed to finish the game.
Only 22 years late ;-)
P.S.: I checked with my MSX friends and no-one was able to finish this game without some form of cheating....